In long term evolution (LTE), in order to achieve a higher system capacity, a higher data transmission rate, reduction of latency in a radio section, etc., a radio communication scheme called 5G has been studied.
In parallel with the study of the 5G radio communication scheme, a radio communication system that supports a 5G radio access technology (new radio access technology (RAT)), an evolved E-UTRA (evolved E-UTRA), an access technology other than that of 3GPP (a non-3GPP access type), etc., have also been studied (for example, see Non-Patent Document 1). According to Non-Patent Document 1, the radio communication system is referred to as a “next generation system.” The next generation system includes a next generation core network.
For the next generation system, similar to the existing LTE, it has been studied to establish a Protocol Data Unit (PDU) session between user equipment and an external network (an external network connected to the outside the next generation network), and to transmit and receive user data using the established PDU session.
In the existing LTE, user equipment attached to a core network (EPC: Evolved Packet Core) is required to always maintain at least one established PDU session. The next generation core network has been studied under the assumption that various types of units of user equipment are supported, such as terminals, e.g., IoT devices, that transmit and receive only a small amount of data at a low frequency and terminals, e.g., smartphones, that frequently transmit and receive a large amount of data.
Thus, in order to support the various types of units of user equipment, the next generation system has been studied such that, after the attach has been completed, user equipment UE establishes a PDU session depending on necessity. Furthermore, since a state exists in the next generation system such that the attach has been completed and no PDU session is established, a system has been studied which is for a server located in an external network to trigger user equipment to establish a PDU session.
FIG. 1 is a diagram illustrating a network triggered on-demand SM setup procedure proposed for 3GPP. An application server (AS) is a server which is located in the external network. A network inter work function (NIWF) is a device that connects the next generation system with the external network. A home subscriber server (HSS) is a server that stores subscriber information. A control plane function (CPF) is a device that processes a call control signal (a C-plane signal). An access network (AS) is a radio network including a base station.